Solid electrolytic capacitors (e.g., tantalum capacitors) are often formed by pressing a metal powder (e.g., tantalum) around a metal lead wire, sintering the pressed part, anodizing the sintered anode, and thereafter applying a solid electrolyte. The solid electrolyte layer may be formed from a conductive polymer, such as described in U.S. Pat. Nos. 5,457,862 to Sakata, et al., 5,473,503 to Sakata, et al., 5,729,428 to Sakata, et al., and 5,812,367 to Kudoh, et al. The conductive polymer electrolyte is traditionally formed by sequentially dipping the part into separate solutions of the monomer used to form the polymer, as well as the catalyst and dopant for the monomer. One problem with this technique is that it is often difficult and costly to achieve a relatively thick solid electrolyte, which is helpful for achieving good mechanical robustness and electrical performance. Also, such polymers can also delaminate from the part during encapsulation of the capacitor, which adversely impacts electrical performance. Some attempts have been made to address this problem. U.S. Pat. No. 6,987,663 to Merker, et al., for instance, describes the use of a polymeric dispersion that covers a surface of the solid electrolyte. The polymeric dispersion generally includes poly(3,-4-ethylenedioxythiophene (“PEDT”) doped with a polymeric anion, such as polystyrene sulfonic acid (“PSS”). Unfortunately, the addition of such a dopant significantly increases the complexity and costs of the dispersion. Furthermore, the ability to form stable dispersions from such PEDOT/PSS systems is often difficult and typically requires the use of surfactants, binders, etc.
As such, a need remains for a solid electrolytic capacitor that possesses good mechanical robustness and electrical performance.